Podsucking bugs

Podsucking bugs (PSB) are considered major pests of all northern region pulse crops except peanuts and chickpea. They reduce crop yield and quality by feeding on developing seeds with piercing-sucking mouthparts. Species include:

  • Green vegetable bug (GVB) Nezara viridula
  • Redbanded shield bug (RBSB) Piezodorus oceanicus
  • Brown shield/stink bug (BSB) Dictyotus caenosus
  • Green shield/stink bug (GSB) Plautia affinis
  • Brown bean bugs (BBB) Riptortus serripes (large) andMelanocanthus scutellaris (small)

Green vegetable bugs (GVB) are the most common species, but others can predominate or contribute to overall PSB pressure.

Brown marmorated stink bug (Halyomorpha halys) is currently not present in Australia, but would also be considered a major podsucking bug pest if it arrives.

Description

Most PBS species are shield shaped. Brown bean bugs are elongated. Younger shield nymphs are round or oval rather than shield-shaped, and bean bug nymphs can easily be mistaken for ants. Young nymphs may aggregate in large clusters, while older nymphs disperse more widely. Nymphs usually change colour as they develop. Final (5th) instar nymphs have less patterning and prominent wing buds.

  Length (mm) Adult Juveniles Eggs
GVB 13-15 Bright green; occasionally yellow or orange. Can darken to purple-brown when overwintering. Orange and brown (and sometimes black) when newly hatched. Later instars are either green or black, with white, cream, orange and red markings

 

 Cream, turning bright orange before hatching. Circular in cross section. Laid in rafts of 50–100 eggs.
RBSB 8-10 Pale green body with pink (female) or cream (male) band across the shoulders and lines along their sides. Orange with black markings when newly hatched. Larger nymphs are pale green with dark-red and brown markings in the centre of the back.

Late autumn nymphs may turn a pale pinkish-brown.

 twin row raft containing 15–40 eggs. Eggs are dark, elliptical (in cross section), and ringed by small spines.
BSB 8 Matte brown Newly hatched nymphs are orange with black markings.

Larger nymphs have dark-brown to black heads and thoraxes, and a pale-brown abdomen with a pale band at the front and transverse dark-brown and pale markings in the centre.

 Pale cream, laid in irregular or twin row rafts of 10–16 eggs
GSB 8 Green body with brown wing covers Cream and yellow with prominent dark markings, changing to mossy green with dark markings on their back Olive-green and laid in small loose rafts of only 5–15 eggs.
SBBB 12 Brown and elongated, long antennae and strong spiny hind legs. Cream stripe along each side (males also have a pale patch on the upper back) and smaller shoulder spines. Nymphs are dark brown and are similar in outline to ants. The abdomen of later instar SBBB is more elongated than LBBB. Shiny olive green laid singly or in small clusters
LBBB 17-18 Brown and elongated, long antennae and strong spiny hind legs. Bright yellow stripe along each side (paler in females), and a prominent spine on each shoulder. Nymphs are dark brown and are similar in outline to ants. The abdomen of later instar SBBB is more elongated than LBBB. Dark purple-brown laid singly or in small clusters

See our PSB gallery for images of various lifestages.

Several predatory shield bugs that can be confused with podsucking bugs, including spined predatory shield bug (Oechalia sp.) and glossy shield bug (Cermatulus sp.).

Most PSBs usually have 5 nymphal stages, and although they can cycle through several generations during summer in Queensland, usually only one generation develops per summer legume crop. However, populations can move progressively from earlier to later plantings, and eventually build to very high levels

Damage

Podsucking bugs can infest crops from flowering onwards, but are primarily pod feeders and prefer well-developed seeds. Crops are at greatest risk from early podfill to late pod ripening. Summer legumes remain at risk until pods become too hard to damage (i.e. very close to harvest).

  • at early podfill, they can potentially reduce yield, but crops are often able to compensate
  • at mid to late podfill, they have a severe impact on seed quality and PSB thresholds are therefore very low
  • brown bean bugs (large and small) are as damaging as GVB.
  • redbanded shield bug and brown shield bug only do ¾ of the damage of GVB but are more difficult to control.
  • GSB damages only 10% as many seeds as GVB
  • nymphs are less damaging than adults.

Early damage reduces yield, while later damage reduces the quality of harvested seed.

  Hosts Damage to pulses compared to GVB
GVB Soybean, mungbean, navy bean, azuki bean, peanut, cotton, sunflower, linseed, maize, and many horticultural crops. 100%
RBSB All summer and winter pulses (except chickpea), and is also a pest in cotton and many horticultural crops. 75%
BSB Soybean, mungbean, navy bean, azuki bean and cotton. 75%
GSB All summer legumes, sorghum, and occasionally cotton. 10%
SBBB All summer and winter pulses (except chickpeas), but favours soybean. Minor pest in cotton and many horticultural crops. 100%
LBBB All summer and winter pulses (except chickpeas), but prefers mungbean, cowpea and adzuki bean. Minor pest in cotton and many horticultural crops. 100%

Monitoring and thresholds

Inspect crops twice weekly from budding until close to harvest:

  • beat sheeting is the preferred sampling method for nymphs and adults
  • visually inspect plants for egg rafts
  • inspect crops twice weekly from budding until close to harvest (the main risk period is at podding)
  • sample early to mid-morning when bugs are more likely to be at the top of the crop.

Podsucking bugs other than GVB are converted to GVB equivalents, and decisions are made based on the GVB thresholds. An online calculator for mungbean and edible soybean is available at the Beatsheet that takes into account both species and development stage.

Edible soybean thresholds are linked to seed quality, and are therefore very low. Crushing and stockfeed soybeans have a higher threshold.

Beat sheet counts may underestimate BBB numbers as adult bugs are very flighty—monitor crops early morning and watch for adults flying away.

Natural enemies

Stink bugs emit a foul smell when disturbed to deter predators, however spiders, ants, and predatory bugs are major predators, particularly of PSB eggs and young nymphs, with mortality sometimes exceeding 90%.

Eggs may be parasitised by tiny wasps such as Trissolcus basalis, T. oenone and Telenomus cyrus. Parasitised eggs turn black.

Final (5th) instar and adult GVB are parasitised by the tachinid fly, Trichopoda giacomellii., which also occasionally attacks RBSB

Management

Spring plantings are at lesser risk than summer planted crops. Avoid sequential plantings of summer legumes, as this allows successive generations of podsucking bugs to build up. Also avoid combining cultivar and planting times that are more likely to lengthen the duration of flowering and podding.

Most products registered in pulses are only for GVB. Always check the product label carefully.

Green stink bugs, brown bean bugs, and to some extent brown shield bugs are usually incidentally controlled by products used against green vegetable bug. However, not all pesticides registered against GVB are effective against redbanded shield bug. Synthetic pyrethroids (e.g. deltamethrin) and the organophosphate trichlorfon give poor RBSB control.

Further information